A power supply system for automotive parts having a rotary component such as, for example, a steering column, as well as for a tire pressure alarm have been proposed wherein the power supply is effected by d slip ring and a brush.
While the proposed power supply systems are simple in construction, by virtue of the fact that the power is supplied by a sliding between a slip ring and a brush, a disadvantage resides in the fact that there is a generation of electrical noise or a contact failure thereby leading to a false actuation of the system or an inferior wear resistance.
In addition to the problem of wear resistance, a further disadvantage of proposed power supply system resides in the fact that there is a demand for a switch construction which enables a control of a plurality of signals such as, for example, the turning on of a headlight, a wiper system, and the like from a steering wheel of a vehicle. If such a switch is incorporated into a conventional system, the slip ring is required to be used in a number of ways thereby leading to problems which include cost, size, electrical noise, and realiability.
In order to cope with the last mentioned disadvantage, a multiple transmission system based on a time sharing has been developed. However, a disadvantage of a multiple transmission system in which a slip ring involves only a power line and a signal line, resides in the fact that such system is easily affected by external noises due to the higher frequency of the signals processed including the electrical noise caused in the slip ring of the power line and the chattering generated in the slip ring of the signal line.
Efforts have been made to eliminate the use of lead wires by, for example, using light or electromagnetic induction for signal transmission of rotary components. However, unless the lead wires for the power lines are eliminated, the realiability and endurance of the transmission system are adversely affected thereby making the wireless transmission of signals useless. This is especially a practical problem in a tire pressure alarm which has been developed for use without needing wires and which includes a dry cell battery as a power supply of the transmission device on the tire side by virtue of a discharge of the power supply battery.
Accordingly, it is an object of the present invention to provide a realiable and durable power supply system for automotive parts having a rotary component which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
In accordance with advantageous features of the present invention, a power supply system is provided in which a pair of coils are opposed to each other around a rotary shaft of a rotary section, with one of the coils being secured to the rotary section and the other coil being secured to a stationary element. The two coils form a DC/DC converter so that, taking advantage of the fact that the degree of magnetic coupling of the coils is maintained constant against a rotation of the coil on the rotary side, a stable power is efficiently supplied to the system on the rotary side in a contactless manner.